In magnetic resonance imaging, a region to be imaged is subject to a main or B0 magnetic field. RF or B1 pulses are transmitted into the region of interest from a quadrature body coil, for example, to excite and manipulate magnetic resonance. Gradient magnetic fields are applied to encode spatial position through phase encoding, frequency encoding, and the like. Magnetic resonance signals from the induced resonance are received with local coils or the quadrature body coil for reconstruction into an image.
Particularly at higher magnetic fields, the body of the patient alters the uniformity of the main, B0 magnetic field and the RF or B1 field.
The B0 magnetic field has been shimmed with active shim coils as well as with passive shims. More specifically, ferrous material is positioned at appropriate positions, generally adjacent the main field coil, in order to shim the B0 field into greater uniformity. Although others have addressed B1 field inhomogeneities, the typical solutions look to improved coil design. For example, B1 field uniformity can be increased through the use of local coils which generate a substantially homogeneous B1 field into small targeted anatomical regions in which the B1 field is designed to be homogeneous.
The present application proposes an improved shimming solution to the above-referenced problems.